Vivotek ND8401 NVR supports Vivotek cameras and ONVIF compatible cameras.
I had to add a Saitell ST-IPC860D-FE camera to the Vivotek NVR which is ONVIF compatible but I keep getting an error "The camera authentication failed. Check user privilege and the correct account or password."
I made sure that the username and password I type on the NVR setting page is correct, I even add another user via the Saitell camera configuration page.
To add a Saitell IP camera which is an ONVIF compatible, make sure to disable the Login Check on the Saitell camera, under Setup -> Network -> Connection -> ONVIF. Then try adding your camera again on the NVR even without typing the camera user name and password.